This invention relates to audio high fidelity apparatus and more particularly to terminators for input and output connectors of audio high fidelity apparatus.
It has been discovered that unterminated input and output ports of audio high fidelity equipment are sources of undesired noise. Noise is believed to be as a result of undesired input common-mode or differential signals due to the lack of a proper load at a signal output and due to high impedance or lack of a signal short to ground at input terminals.
A direct short to ground at an input terminal is an ideal termination. Unfortunately, there is typically a length of some significance between a chassis connection and the input to the first circuit element such that a receiving antenna and detector or the like is created for spurious signals. A similar problem is evident in the signal line from an output terminal of a circuit to an output jack on the chassis of the equipment. The problem is aggravated where the output port of a circuit is coupled to multiple output jacks in parallel. Some of the output jacks may be properly loaded while others are not, giving rise to open circuit signal reflections which can cause undesired oscillations ("ringing") in the signal lines due to transmission line effects. The distortion may be further aggravated by negative feedback loops between the output terminals wherein the spurious signals are present and thereby coupled into the input through the feedback signal lines.
What is needed is a mechanism for minimizing the undesired effects caused by improperly terminated input and output ports in an audio high fidelity circuit.
It is known to provide impedance matched terminations at the outputs of driving circuitry, particularly in high frequency equipment where impedance matching, is of critical concern. Nevertheless, it has been discovered that impedance matching is important even at low frequencies in relatively long wave or audio frequency signal applications. Not commonly recognized in the audio high fidelity arts has been the benefit of rf suppression in addition to the benefit of proper impedance matching.